1. Field of the Invention
The present invention relates to the field of electron microscopy. More particularly, the present invention relates to a system and a method for magnetic and spectroscopic imaging.
2. Description of the Related Art
Magnetic media presently used for disk drives are thin films that have grains that are about 15 nm across. Soon the grain size will be under 10 nm. To better understand how the magnetic microstructure of the media affects magnetic recording processes, magnetic imaging having a resolution of less than 5 nm is required. Currently, only transmission electron microscopy (TEM) provides an imaging resolution that is on the order of 5 nm. TEM, however, is limited by requiring a sample to be processed to be about 100 nm thick. Further, TEM is insensitive to ultra-thin films, that is, films, that are on the order of 20 nm thick or less.
Many techniques have been developed for extracting various types of image information from a scanning probe microscope (SPM). One technique uses a scanning near-field optical probe, but has a low efficiency for collecting emitted photons. Collection efficiency is improved by using photoemission so that electrons are emitted from the surface of a sample and collected using a positively-biased scanning probe, such as disclosed by K. Tsuji et al., X-Ray Excited Current Detected with Scanning Tunneling Microscope Equipment, Jpn. J. Appl. Phys, Vol, 34, pp. LI 506-LI 508, 1995. Nevertheless, this approach is limited by the noise of the collection current amplifier (Johnson noise). Another limiting factor with this approach in practice is an interfering signal caused by emission from the scanning tip. There are also difficulties associated with sufficiently limiting the collecting area for achieving good spatial resolution.
Stohr et al., Element-specific Magnetic Microscopy Using Circularly Polarized X-rays, Science, Vol. 259, p. 658, 1993, discloses a photoemission microscope that is capable of magnetic imaging by using conventional electron microscope optics for imaging photoemitted electrons. This approach efficiently collects electrons and has a theoretical resolution of about 10 nm, but the high voltages inherent in this approach makes the microscope susceptible to breakdown and arcing.
What is needed is a technique having nm-scale resolution for imaging magnetic and spectroscopic features that does not require sample thinning and can image an ultrathin film without the application of high voltages,